Securely passing arguments when opening a pipe to a program

[Joonas Paalasmaa]

I am using Gnokii to send SMS messages with Python. Gnokii is started
with 
popen2.popen2 like this:

gnokiiRead, gnokiiWrite = popen2.popen2("gnokii --sendsms %s" %
phonenumber)
gnokiiWrite.write(message)
gnokiiWrite.close()
response = gnokiiRead.read()
gnokiiRead.close()

The problem is that the phonenumber string is not safe; it can even be
"000; rm -fR ~/*". How can I securely pass arguments when opening the
pipe?
Is there a way to pass the arguments like in os.execv.

- Joonas